I am currently reading On the Spirit and the Letter with students. He says much about the Law in various places in his writings. But here (chapter 23) he says:
"The apostle seems to rebuke and correct those who were persuaded to receive circumcision in that by the term “law” he refers to circumcision and other such observances of the law. Christians do not now observe them, since they were foreshadowings of what was to come. And they now actually possess what was promised symbolically through those foreshadowings."
He then goes on to say:
"The apostle, nonetheless, wanted us to understand that the law, by which he says that no one is justified, is found not only in those sacraments which they had as symbols of what was promised, but also in those works which amount to a righteous life for whoever does them."